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DIY Stompboxes => Building your own stompbox => Topic started by: jherron on January 22, 2005, 10:37:07 PM

Title: Mini Booster not passing signal
Post by: jherron on January 22, 2005, 10:37:07 PM
OK, so this is my first build, and I  can't figure out what is wrong. Everything seems to be wired correctly and in testing, the continuity seems fine as well. However, when using an auidio probe the signal seems to stop at the drain of the first transistor (j201). I'm using the schem and layout from ggg for the AMZ minibooster.  Any help would be greatly appreciated.
Title: ....
Post by: petemoore on January 22, 2005, 10:41:32 PM
J201: make sure of the pinout. Unless build from the schematic with a 'twist', you'll have to twist the G/S leads of the Q to correct pinout.
 Modding your own Mu Amp GEO, Top Jfet arrangement sets bias of bottom Q.
 What are the bias readings ?
Title: Mini Booster not passing signal
Post by: jherron on January 22, 2005, 10:56:33 PM
I'm pretty sure of the pinout, from the data sheet. Still, I socketed the transistors and tried them the other way as well. Not sure how to check the bias though  :oops: ... I'm still pretty green.
Title: .
Post by: petemoore on January 22, 2005, 11:22:08 PM
Set DMM: 20vdc range
 Clip black meter lead to ground
 Touch red lead to Top Q D take reading, write it down, Repeat for Q1 G and Q1 Source, also take Q2 D, G and S readings.
 While you have black DMM lead to ground, switch DMM to 'diode' [continuity test beeps when red and black leads connect], and check all ground points.
 I like to test that Battery clip + and _ actually make board + and _.
 Post the voltage readings.
  http://www.diystompboxes.com/pedals/debug.html
Title: Mini Booster not passing signal
Post by: jherron on January 22, 2005, 11:47:11 PM
Ok, here's what I got:

Q1  D-  6.07
     S-  4.02
     G-  3.04

Q2  D- 4.02
     S- .99
     G-  0

Ground points seem fine also
Title: Mini Booster not passing signal
Post by: R.G. on January 23, 2005, 07:52:56 PM
Q1 d seems awfully low.
Title: ...
Post by: petemoore on January 23, 2005, 11:59:25 PM
Try this one ... Ill check it.
 Click on GeoFex at top of this page, scroll down to 'mod your own mu amp' click on that.
 Include measured battery voltage with the readings of Q's pins.
Title: Mini Booster not passing signal
Post by: javacody on January 24, 2005, 11:55:32 AM
Did you use a 3.3uF Non Polar cap for C2?
Title: Mini Booster not passing signal
Post by: jherron on January 24, 2005, 12:57:05 PM
Quote from: javacodyDid you use a 3.3uF Non Polar cap for C2?

Yes, however I originally had the wrong value there.
Title: ...
Post by: petemoore on January 24, 2005, 01:00:47 PM
State the Value used ??
Title: Re: ...
Post by: jherron on January 24, 2005, 01:47:52 PM
Quote from: petemooreState the Value used ??
When I first built it (before I posted here), I had a cap that I thought was the 3.3 np electro.  I think it was 100uf or something. After I figured that out (and put in the correct cap), I changed the transistors since I wasn't sure if the wrong cap could have damaged the original transistors.
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